This invention relates to the field of guidewires for advancing intraluminal devices such as stent delivery catheters, balloon dilatation catheters, atherectomy catheters and the like within body lumens.
Conventional guidewires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to a rounded plug at the distal end of the flexible body.
In a typical coronary procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into a patient""s peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient""s coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the procedure is performed.
A requirement for guidewires is that they have sufficient column strength to be pushed through a patient""s vascular system or other body lumen without kinking. However, they must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guidewires to make them more suitable for their intended uses, but these two properties are for the most part diametrically opposed to one another in that an increase in one usually involves a decrease in the other.
Further details of guidewires, and devices associated therewith for various interventional procedures can be found in U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.); U.S. Pat. No. 5,135,503 (Abrams); U.S. Patent 5,341,818 (Abrams et al.); and U.S. Pat. No. 6,345,945 (Hodgson et al.) which are hereby incorporated herein in their entirety by reference thereto.
Pseudoelastic alloys can be used to achieve both flexibility and strength. When stress is applied to NiTi alloy exhibiting pseudoelastic characteristics at a temperature at or above which the transformation of martensite phase to the austenite phase is complete, the specimen deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenite phase to the martensite phase, As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress are necessary to cause further deformation.
If the load on the specimen is removed before any permanent deformation has occurred, the martensitic specimen will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensite phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant until the transformation back to the austenite phase is complete, i.e. there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as pseudoelasticity. These properties to a large degree allow a guidewire core of a psuedoelastic material to have both flexibility and strength. However, psuedoelastic alloy components are typically difficult to join or secure to other components. This is due primarily to a tenacious oxide layer that develops on the surface of some such alloys, particularly those containing titanium.
Prior methods of pre-treatment for securing subassemblies to a distal core made of pseudoelastic alloys such as NiTi include molten or fusion salt etching and then pre-tinning the core to facilitate forming a strong bond, as seen in U.S. Pat. No. 6,695,111 to Nanis et al. which is hereby incorporated in its entirety by reference. While this method represents a significant advance, what has been needed is a method for manufacturing a guidewire with a superelastic or psuedoelastic component which will allow the component to accept a weld, solder or adhesive joint with ease of manufacture and low cost. It is also desirable to have a manufacturing process in which the mechanical properties of psuedoelastic and high strength alloys can be combined.
The present invention is directed to an intracorporeal device, preferably a guidewire, and method for making the device. The guidewire has an elongate core member with a proximal section and a distal section. The elongate core has an inner core element of a desired metal and an outer layer of material disposed about the inner core element. The outer layer of material is typically applied to the inner core element as a braid which is then cold drawn through a die which conforms and secures the outer layer to the inner core element. The outer layer of material may be cold drawn to a smooth continuous layer, or may be cold drawn to a lesser extent where the outer layer maintains a braided flattened configuration.
In an alternative embodiment of the invention, an elongate core member has a second outer layer of material applied to an inner core element and a first outer layer of material which may be drawn filled tubing. The drawn filled metallic tubing preferably consists of an inner core element of stainless steel and a first outer layer of psuedoelastic alloy, normally consisting of NiTi alloy disposed about the inner core element. The second outer layer of braided stainless steel is applied and cold drawn through a die so as to create an elongate core member having a layer of NiTi alloy sandwiched between an inner core element and an outer layer of stainless steel. When the distal section of this elongate core member is tapered to a distally smaller cross section, the various layers of the elongate core member are exposed.
Typically, a flexible body is disposed over and secured to at least a portion of the distal section of the elongate core member. The flexible body can be a helical spring but can also be a polymer jacket of material that can be thin or sufficiently thick to provide a diameter similar to that of the proximal section.
The distal end of the helical coil, or other flexible body, is preferably secured to a distal end of the elongated core member, by soldering, brazing, welding, bonded polymeric materials or other suitable means.
The inner core element, which is preferably stainless steel or other suitable high strength bondable or solderable material, is exposed at the distal end of the elongate core member as a result of the tapering of the distal section. Exposure of the inner core element allows the distal end of the flexible body to ha bonded or soldered to the distal end of the bondable or solderable material of the inner core element. A proximal end of the flexible body is preferably bonded or soldered to a distal section of the second outer layer of material. Preferably, the second outer layer of material is comprised of stainless steel or some other suitable bondable or solderable material. In this way, the flexible body will have its distal and proximal ends secured to bondable or solderable materials. If the first outer layer of material is made of a pseudoelastic alloy, a desired amount of the distal section can exhibit mechanical properties of the pseudoelastic alloy which comprises the majority of the distal section material. This results in high strength bonding or soldering between the guidewire components, smooth flexibility transitions in the elongate core member and the desired pseudoelastic mechanical characteristics in the distal section of the elongate core member. In addition to solderablity and bondability, the outer layers of material may be selected for desired mechanical strength properties. For example, a second outer layer of material may be made from a precipitation hardenable alloy such as MP35N in order to give the proximal section of the elongate core member a desired amount of strength.